Inspection of the states of a vehicle including the air pressure of tires has long been an indispensable task for ensuring its safe running. However, since manual inspection of a vehicle costs much labor and time, vehicle monitoring systems were developed for automatic monitoring the states of vehicles including the air pressure of tires, and have begun to be used on combination vehicles (hereinafter the pulling vehicle in the combination will be referred to as the tractor and the pulled vehicle, as the trailer).
Already proposed such vehicle monitoring systems include one in which wireless signals are transmitted from sensor units (detecting devices) for detecting the pressure and temperature of each tire of the tractor and the trailer to the cab unit (one relaying device) either via a trailer transponder (another relaying device) or directly and the information received by the cab unit (the one relaying device) having received the information on pressures and temperatures is displayed on a display (display device) to provide an alarm or the like to the driver (see Patent Document 1 for instance), and another in which each tire is equipped with a tag (detecting device) combining a responder, a pressure sensor and so forth, an RF (radio frequency) signal measured and transmitted by each tag (detecting device) is received by a monitor (another relaying device) disposed in the vicinity of each tire, each monitor is connected via a data bus to a computer (one relaying device) provided in the vehicle, and the computer (the one relaying device) deciphers the RF signals transmitted from the tag (detecting device) of each tire and outputs the information to a central display (display device) (see Patent Document 2 for instance).
However, in the vehicle monitoring system according to Patent Document 1 or Patent Document 2, since information transmitted by the detecting devices are recognized on the basis of identifying information of detecting devices registered with the one relaying device and displayed on the display device, when the trailer linked to the tractor is to be changed, there is a fear that, unless identifying information of the plurality of detecting devices disposed on the new trailer is registered with the one relaying device anew, it may be impossible to recognize information transmitted by each detecting devices on the trailer and display it on the display device disposed on the trailer.
As a solution to this problem, it is proposed to set, when the trailer linked to the tractor is to be changed, environmental data for the replacing trailer by connecting an electronic key storing environmental data including identifying information of each module (detecting device) of the trailer to a central unit (one relaying device) of the tractor (see Patent Document 3 for instance).
Patent Document 1: National Publication of International Patent Application No. 2002-516399
Patent Document 2: National Publication of International Patent Application No. 2003-509260
Patent Document 3: Japanese Patent Publication No. H6-255436